The present invention relates to a digital sampling instrument and more particularly to a digital sampling keyboard instrument.
Digital sampling keyboard instruments are known in the prior art to provide accurate generation of virtually any sound, such as piano, (violin or any other type of sound, for that matter). Typically, an analog audio sound is digitized and stored in a sound memory and then played out by a user, as desired. With prior art instruments, in order to change the pitch of a particular sound (such as increasing the pitch of a violin sound) the prior art has, in some approaches, changed the spacing interval between digital samples. For example, in order to increase the pitch of a particular sound, the sampling rate is changed from, for example, 50 microseconds to 40 microseconds. This approach, while generally adequate, requires expensive asynchronous hardware.
Another approach is to effectively "skip" or "duplicate" particular digital samples, which effectively increases the pitch, but also generates unwanted distortion.
Another approach is to oversample the digital samples, which in effect divides up a pitch period (such as a pitch period of 50 microseconds) into a smaller number of subperiods. For example, a pitch period of, say, 20 subperiods can be sampled within 19 periods, thus effectively increasing the pitch of a particular sound, while reducing or limiting the distortion (which can still be present).
As is also known in the prior art, the digital samples stored in a sound memory are generally stored as PCM data. In order to provide suitable fidelity in the actual audio sound generation, prior art approaches can introduce an unwanted or undesirable "clicking" sound. This is because of what can happen when PCM encoding an audio sound (for example, an audio sine wave). When there is a sudden change of the volume (such as by a step function), this can introduce an undesired clicking noise into the volume scaling, which again affects the fidelity of the sound generation.